Re: [PATCH bpf-next v8 2/2] selftests/bpf: Add an usdt_o2 test case in selftests to cover SIB handling logic

On Thu, Aug 14, 2025 at 06:45:04AM +0000, Jiawei Zhao wrote:

When using GCC on x86-64 to compile an usdt prog with -O1 or higher optimization, the compiler will generate SIB addressing mode for global array and PC-relative addressing mode for global variable, e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".

In this patch:

• add usdt_o2 test case to cover SIB addressing usdt argument spec handling logic

hi, on my setup (gcc15) the test generates ust register argument:

stapsdt 0x0000002a NT_STAPSDT (SystemTap probe descriptors) Provider: test Name: usdt1 Location: 0x00000000007677ce, Base: 0x00000000035bc728, Semaphore: 0x0000000000000000 Arguments: 8@%rax

7677c6: 48 8b 04 c5 20 49 9c mov 0x39c4920(,%rax,8),%rax 7677cd: 03 7677ce: 90 nop

I'm not sure if there's reliable solution to generate SIB argument from gcc, maybe we could generate all in assembly, but that might get complicated

jirka

Signed-off-by: Jiawei Zhao phoenix500526@163.com

tools/testing/selftests/bpf/Makefile | 1 + .../selftests/bpf/prog_tests/usdt_o2.c | 69 +++++++++++++++++++ .../selftests/bpf/progs/test_usdt_o2.c | 37 ++++++++++ 3 files changed, 107 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o2.c create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o2.c

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 4863106034df..24ff1a329625 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -760,6 +760,7 @@ TRUNNER_BPF_BUILD_RULE := $$(error no BPF objects should be built) TRUNNER_BPF_CFLAGS := $(eval $(call DEFINE_TEST_RUNNER,test_maps))

# Define test_verifier test runner. # It is much simpler than test_maps/test_progs and sufficiently different from # them (e.g., test.h is using completely pattern), that it's worth just diff --git a/tools/testing/selftests/bpf/prog_tests/usdt_o2.c b/tools/testing/selftests/bpf/prog_tests/usdt_o2.c new file mode 100644 index 000000000000..f02dcf5188ab --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/usdt_o2.c @@ -0,0 +1,69 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2025 Jiawei Zhao phoenix500526@163.com. */ +#include <test_progs.h>

+#include "../sdt.h" +#include "test_usdt_o2.skel.h"

+#if defined(__GNUC__) && !defined(__clang__) +__attribute__((optimize("O2"))) +#endif

+#define test_value 0xFEDCBA9876543210ULL +#define SEC(name) __attribute__((section(name), used))

+int lets_test_this(int); +static volatile __u64 array[1] = {test_value};

+static __always_inline void trigger_func(void) +{

• /* Base address + offset + (index * scale) */
• for (volatile int i = 0; i <= 0; i++)

• STAP_PROBE1(test, usdt1, array[i]);
  

+}

+static void basic_sib_usdt(void) +{

• LIBBPF_OPTS(bpf_usdt_opts, opts);
• struct test_usdt_o2 *skel;
• struct test_usdt_o2__bss *bss;
• int err;
• skel = test_usdt_o2__open_and_load();
• if (!ASSERT_OK_PTR(skel, "skel_open"))

• return;
  

• bss = skel->bss;
• bss->my_pid = getpid();
• err = test_usdt_o2__attach(skel);
• if (!ASSERT_OK(err, "skel_attach"))

• goto cleanup;
  

• /* usdt1 won't be auto-attached */
• opts.usdt_cookie = 0xcafedeadbeeffeed;
• skel->links.usdt1 = bpf_program__attach_usdt(skel->progs.usdt1,

• 				     0 /*self*/, "/proc/self/exe",
  

• 				     "test", "usdt1", &opts);
  

• if (!ASSERT_OK_PTR(skel->links.usdt1, "usdt1_link"))

• goto cleanup;
  

• trigger_func();
• ASSERT_EQ(bss->usdt1_called, 1, "usdt1_called");
• ASSERT_EQ(bss->usdt1_cookie, 0xcafedeadbeeffeed, "usdt1_cookie");
• ASSERT_EQ(bss->usdt1_arg_cnt, 1, "usdt1_arg_cnt");
• ASSERT_EQ(bss->usdt1_arg, test_value, "usdt1_arg");
• ASSERT_EQ(bss->usdt1_arg_ret, 0, "usdt1_arg_ret");
• ASSERT_EQ(bss->usdt1_arg_size, sizeof(array[0]), "usdt1_arg_size");

+cleanup:

• test_usdt_o2__destroy(skel);

+}

+void test_usdt_o2(void) +{

• basic_sib_usdt();

+} diff --git a/tools/testing/selftests/bpf/progs/test_usdt_o2.c b/tools/testing/selftests/bpf/progs/test_usdt_o2.c new file mode 100644 index 000000000000..14602aa54578 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_usdt_o2.c @@ -0,0 +1,37 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */

+#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include <bpf/usdt.bpf.h>

+int my_pid;

+int usdt1_called; +u64 usdt1_cookie; +int usdt1_arg_cnt; +int usdt1_arg_ret; +u64 usdt1_arg; +int usdt1_arg_size;

+SEC("usdt") +int usdt1(struct pt_regs *ctx) +{

• long tmp;
• if (my_pid != (bpf_get_current_pid_tgid() >> 32))

• return 0;
  

• __sync_fetch_and_add(&usdt1_called, 1);
• usdt1_cookie = bpf_usdt_cookie(ctx);
• usdt1_arg_cnt = bpf_usdt_arg_cnt(ctx);
• usdt1_arg_ret = bpf_usdt_arg(ctx, 0, &tmp);
• usdt1_arg = (u64)tmp;
• usdt1_arg_size = bpf_usdt_arg_size(ctx, 0);
• return 0;

+}

+char _license[] SEC("license") = "GPL";

2.43.0